Most RV owners couple trailers to their vehicles only occasionally. Accordingly, they may not be entirely familiar with the process of coupling a trailer to a towing vehicle, and thus may couple their trailer to their vehicle incorrectly. In some instances, incorrect trailer coupling can make it possible for the trailer to become detached from the towing vehicle (referred to as a “dropped trailer”), which can cause considerable damage to both the towing vehicle and the trailer. If a trailer is dropped at highway speeds, the event can lead to tragic results.
One of the more common causes of dropped trailers is improper alignment of the trailer and towing vehicle during coupling. For example, some fifth wheel hitch designs permit the trailer kingpin to be inserted into the throat of the hitch without regard to the elevation of the kingpin relative to the hitch. The kingpin thus may inadvertently be placed on top of the jaw member of the hitch, rather than in a position wherein the jaw member would be able to close around (or otherwise capture) the kingpin. This condition (referred to in the industry as “high pinning”) may be exacerbated in fifth wheel hitches that permit closure of the jaw member even when the kingpin is not in the correct position. In such hitches, the user may be given the impression that a trailer is safely coupled to the towing vehicle and locked in place, when it is not.
A dropped trailer also may occur when a trailer kingpin is not fully engaged by the jaw member, or where a user fails to lock the hitch once the kingpin is in place. For example, a user may attempt to couple the trailer to the towing vehicle when the jaw member is already closed. The kingpin thus may contact the closed jaw member and stop, before fully entering the throat of the hitch. Under these circumstances, the kingpin would not be captured by the jaw member. Similarly, a user may fail to move the vehicle far enough back to bring the kingpin fully within the throat of the hitch, and thereafter, may close the jaw member without capturing the kingpin.
Hitch manufacturers often recommend testing the hitch coupling before towing a load. A user thus may pull the towing vehicle forward slightly before locking the hitch (referred to as a “tug-pull test”). With the trailer wheels chocked, the trailer shouldn't move and the user should feel the resistance of the trailer. Unfortunately, not all users perform such a procedure, and even if they do, the test is not fool proof. In some instances, the kingpin may be secured sufficiently to feel solid during a tug-pull test (e.g., due to frictional forces), but may not be truly secured. A user relying on a tug-pull test thus may lock the hitch under the illusion that the trailer is safely secured in place. The towing vehicle then may be driven until the load is great enough to dislodge the trailer from the hitch, resulting in a dropped trailer.